Heat responsive device



Filed April 30, 1936 3nventor '(Ittomeg Patented Mar. i2, 194@ STTESPATNT OFFICE Radio Corporation of America, a

of Delaware corporation Application April 30, 1936, Serial No. 77,245

4 Claims.

This invention relates to heat-responsive devices and particularly tothermostats, thermocouples, etc., operating in vacuo or in an attenuatedatmosphere of gas.

The prior art is replete with thermostats and like heat responsivedevices contained in sealed glass envelopes. Usually the glass envelopeor tube is highly evacuated or it contains a rarefied gas, such mode ofconstruction having been found efiective in reducing sparking betweenthe circuit closing members. One disadvantage of prior art thermostatsof the type described, which is V especially apparent whenthe thermostatis used in connection with apparatus requiring rapid and accurateresponse to variations in the temperature of the ambient medium, is thefact that the'vacuum (or rarefied gas) within the envelope inhibits thetransmission of heat to the thermal responsive elements within the tubeat a rapid rate. Prior art tube-type thermostats may therefore be saidto exhibit an inherent timelag.

An object of the invention is to provide a hermetically sealed heatresponsive device, the operation of which is characterized by minimumtime lag.

Another object of the-invention is to provide a heat responsive devicecontained in a sealed envelope wherein the transmission of heat from theambient medium to the area immediately adjacent the active elementswithin the envelope is efiected at a rapid rate.

Another object of the invention is to provide a sealed heat responsivetube having an ambient thermal compensator incorporated therein.

Another object of the invention is, to provide an extremely accurate,rapid-acting, inexpensive and trouble-free thermostat.

The above and other objectsare accomplished in accordance with theinvention by providing a metallic heat-conducting member in heatexchange relation with the thermal responsive element and the exteriorof the envelope containing the element. The metallic heat-conductingmember may constitute at least a portion of the envelope or tube. It maybe a rod or ribbonlike member or it may be a metal sheath, positionedadjacent the heat responsive element, and provided with an extensionpassing through glass or metal wall of the tube. Again, if the device isprovided with an interior electrode supporting frame the frame itselfmay be provided with an external heat-conducting lead. If desired anumber of spokes or fins radiating from the compensator to the tube wallmay be provided for increasing the heat exchange ratio between theexterior wall and the heat responsive element.

Certain details of construction together with other objects andadvantages will be apparent and the invention itself will be bestunderstood 5 by reference to the following description and to theaccompanying drawing, wherein Figure 1 is a sectional elevation of athermostat enclosed in a metal tube,

I Fig. 2 is a sectional elevation of a thermostat 1o enclosed in a metaltube and including an auxiliary thermal compensator and externalconnection therefor,

Fig. 3 is a sectional elevation of a thermostat enclosed in a metal tubeand including a plurality, 15 of thermal compensators connected directlyto the wall of the tube,

Fig. 4 is a cross-sectional view taken on the line 4-4 of Fig. 3,

Fig. 5 is a sectional elevation of a thermostat 2o enclosed in a glasstube and including a thermal compensator in the form of a sheath'withinthe tube, and

Fig. 6 is a sectional view of an adjustable thermostat of a known typewherein the thermal 25 compensator of the-present invention isconstituted in part by the electrode-supporting struc- 'ture.

Referring now in detail to Fig. 1 which shows a simplified form of theinvention. An envelope 30 or tube formed of steel or'other excellentheat conducting metal is designated 'A. The tube contains a pair ofinwardly extending leads B and D, which enter the tube through ceramicbeads C and E in the base of the tube and support a pair of parallellyarranged contact arms F and H. Arm F is the heat-responsive element; itis constituted by a bi-metallic laminated strip which changes itscontour under varying temperatures to open or close, as the case may be,the 40 contact members G and J. The contact arms F and H are maintainedin spaced relation by means of an electrical insulator K, washer L andscrew or rivet M. The tube A may be highly evacuated or it may contain afilling of hydrogen gas or the like, at an attenuated pressure.Evacuation is effected and the gas sealed in the tube through a latersealed orifice'N in the tube wall. The improved operatingcharacteristics of the device of Fig. 1 over glass enclosedthermo-regulators may be attributed to the fact that the metal wall ofthe tube is a far betterconductor of heat than is the glass of prior artdevices, consequently the temperature adjacent the bimetallic strip Fand the actuation of this strip,

will follow temperature variations in the ambient medium exterior of thetube more rapidly and closely. When it is required that operation of thestrip F be affected in part by the temperature of an ambient mediumremote from the immediate proximity to the tube A, a heat conductinglead P may be provided from the remote point to the outer wall of thetube, and joined thereto as by a Weld or by solder. One such use isdescribed in copending application Serial No. 61,834, (RCAV-4353) toSamuel A. Bokovoy, filed January 31, 1936, and assigned to RadioCorporation of America.

In Fig. 2 the heat transfer member, here designated 2P, is sealed withinthe metal tube 2A, instead of being fixed to the outside of the tube asin Fig. 1. Member 2P is in the form of a strip or ribbon of metalpositioned between and in close heat exchange relation with the contactarms 2F and 2H. It is supported on the insulator 2K which carries thecircuit closing current carrying arms 2F and 2H and has an external heatconductive connection 2B which enters the tube through a ceramic seal2S. The provision of this auxiliary heat transfer member 2P within thetube aids in varying the temperature immediately adjacent thebi-metallic strip 2F in accordance with temperature variations in theexternal ambient medium.

The tube thermostat of Figs. 3 and 4 is'provided' with three ambientthermal compensator strips. The center strip 3P may be similar in allrespects to that described in connection with Fig. 2, that is to say, itis mounted within a metal tube SA on an insulator 3K; it is parallellyarranged with respect to the contact arms 3F and 3H and has an externalconnection 3R which extends through a ceramic seal 3S in the base orWall of the tube. The other compsenator strips are designatedrespectively, 3T and 3U and like strip 3P are mounted on the insulator3K. Unlike strip 3P they are provided with no external leads but aremaintained in heat transfer relation with the inner wall of the tube bymeans of a plurality of heat conducting metal spokes or 'fins 3V. Heattransmitted or dissipated through compsenator strip 3P, through lead 3R,and strips 3T and 3U through fins 3V, ensure a temperature adjacent thethermal responsive arm 3F closely approximating that of the externalambient medium.

The thermostat of Fig. 5 is enclosed in a glass tube 5W which like themetal tubes of Figs. 1 to 4 may contain a rarefied gas or it may hehighly evacuated. Here the ambient thermal compensator takes the form ofa metal sheath 5X surrounding the electrodes 5F and 5H within the tube.This sheath may be contiguous the inner wall of the tube, as shown, orit may be mounted on the insulator 5K in a manner similar to that bywhich the strips 3T and SW of Fig. 3 are mounted. A heat conducting lead5R, which may be in the form of a metal ribbon, sealed through the glassenvelope, is provided for connecting" tact point 62. The other contact63 is fixed on a bent arm 64 against which the end of a threadedadjusting rod 65 rests. of threaded rod 65 is a disc 66 of magneticmaterial which, when subject to the field of an external magnet (notshown), may be moved to vary the spring action of the bent contact arm64 and to thereby alter the spacing of the contacts 62, 63. The contactarms BI and 64 and the adjusting rod 65 are mounted on a frame 61 as bymeans of insulating pieces 68, 69, I0 and II and rivets 12. A frictionspring I3 on the frame presses against the adjusting rod 65 to preventundesired movement thereof. The insulating pieces 68 to H forming partof the frame 61 fit against the curved inner walls of the tube 60 andare maintained thereagainst by the action of a holding spring I whichprevents dislocation and shock movement of the assembly.

The current carrying leads for contacts 62 and 63 are designated 14 and15, respectively. The third external lead 16 is the heat transfer lead;it connects the frame 61 within the tube, with the external ambientmedium and, as in the previously described embodiments of the inventionensures a desired heat-transfer-ratio between this medium and thethermal responsive element within the tube.

While the invention has been described as applied to a thermostat, it isto be understood that it is not to be limited by such application as thedisclosure in this respect is merely illustrative for purposes ofexplaining the inventive concept. Obviously, the thermal compensator ofthe invention may be embodied in tubes containing mercury relays,thermocouples and other known types of heat responsive devices. Further,the invention is not to be limited to the use to which the completeinstrument is put. The use described in application Serial No. 61,834,(which discloses a thermal ambient compensator embodied in a. constanttemperature cabinet) is but one of many uses to which the invention maybe put.

Another very useful application to which the invention may be put is inconnection with control systems for house-heating oil-burners and thelike. When so applied the thermostat or other instrument embodying theinvention may be placed, for instance, on the cellar wall and theambient thermal compensator connected by a comparatively short heatconducting insulated lead to the exterior of the building. By a properselection of the material and mass of the lead and compensator anydesired heat transfer ratio may be established between the outer ambientmedium and the thermostatic (or other) control and the operation of theburner controlled in accordance with variations in the external ambienttemperature.

Air conditioning systems may likewise employ temperature responsivetubes embodying the ambient thermal compensator'of the present inventionto advantage.

Other modifications and applications of the invention will suggestthemselves to those skilled in the art. It is to beunderstood,therefore, that the foregoing is to be interpreted as illustrative andnot in a limiting sense except as required by the prior art and by thespirit of the appended claims.

What is claimed is:

1. The combination with a thermal responsive element enclosed in asealed glass enevelope of an electrically separate heat conductingmember Fixed on the other end in the form of a metallic sheath at leastpartially surrounding said thermal responsive element and having apermanent heat conductive connection thereof communicating with theexterior of said envelope which heat conducting member is in closeproximity of said element and having a portion thereof in direct heatexchange relation with the ambient medium outside of said envelope formaintaining a predetermined ratio between the temperature of saidelement and the temperature of the external ambient medium.

2. The combination with a thermal responsive element enclosed in asealed metal envelope of an electrically separate heat conducting memberin close proximity to said element within said metal envelope, and aheat conductive connection connecting said member to the inner wall ofsaid metal envelope for maintaining a predetermined ratio between thetemperature of said thermal perature of said thermal responsive elementand the temperature of the external ambient medium. 4. The combinationwith a thermal responsive device supported upon a metal frame within asealed envelope of a ribbon of heat conducting material connected tosaid frame and communicating with the exterior of said envelope.

SAMUEL A. BOKOVOY.

